Efficient catalytic activation of Suzuki–Miyaura C–C coupling reactions with recyclable palladium nanoparticles tailored with sterically demanding di-n-alkyl sulfides

Abstract

n-Bromodocosane reacts with Na 2 S, generated in situ by the reduction of elemental sulfur with NaBH 4 , to give n-didocosyl sulfide (L1), which acts as a protector for palladium nanoparticles (2-7) that are prepared using different palladium precursors in the presence of L1 (Pd : L1 ratio 1 : 2 and 4 : 1). The NPs have been characterized with powder X-ray diffraction, SEM, EDX, UV-vis spectroscopy and HRTEM. The size (nm) ranges for the majority of spherical NPs 2-7 are $18-19, 4-5, 5-7, 4-6, 7-9 and 4-6 respectively. The precursor of palladium affects the size, shape and dispersion of the NPs. When [Pd(CH 3 CN) 2 Cl 2 ]/ Na 2 PdCl 4 was used as a precursor, uniformly dispersed NPs of narrow size range were obtained. L1 and its complex [Pd(L1) 2 Cl 2 ] (1) have also been synthesized by the reaction of Na 2 PdCl 4 with L1 and characterized with 1 H and 13 C{ 1 H} NMR spectroscopy. The NPs show good catalytic activity for the Suzuki-Miyaura coupling (SMC) of various aryl chlorides/bromides with phenylboronic acid at low catalyst loading (0.1-0.5 mol% of Pd). The conversion is good for some aryl halides in a short reaction time of the order 1-2 h. Among 2-7, the highest activity is observed for Pd NPs obtained from Na 2 PdCl 4 , which is probably due to uniformity in their size and dispersion. The distinct advantage of NPs 2-7 is that they can be separated and reused at least up to five times. The complex 1, equivalent to 0.001 mol% Pd, is efficient for the SMC of some aryl halides, as good conversion into coupled products has been observed. Two phase tests, conducted for 1 and 3, suggest the contribution of both homogeneous and heterogeneous catalytic pathways in overall catalysis. ; Fax: +91 11 26581102; Tel: +91 11 26591379 † Electronic supplementary information (ESI) available: Spectral data of L1 and 1;SEM, EDX and powder XRD of NPs. See

Ultra-small palladium nano-particles synthesized using bulky S/Se and N donor ligands as a stabilizer: application as catalysts for Suzuki–Miyaura coupling

“…Some Pd(0) NPs stabilized with mono dentate organochalcogen ligands 30,31 are reported earlier. These NPs showed excellent activity towards the coupling of aryl bromides and iodides.…”

“…[22][23][24][25][26][27][28][29] Presence of neutral chalcogen donor in stabilizers affects the catalytic efficiency, composition, size, recyclability, and dispersion of the nanoparticles to a great extent. 30,31 The use of organochalcogen ligands in the development of molecular catalysts has been studied in a variety of cases. [22][23][24][25][26][27][28][29] However, the use of such ligands in the stabilization of nanoparticles is limited.…”

“…[22][23][24][25][26][27][28][29] However, the use of such ligands in the stabilization of nanoparticles is limited. 30,31 To the best of our knowledge, no such compound containing a combination of hard-hard or hard-so donors have been reported for this purpose. Thus, in this article, we are reporting the synthesis (Scheme 1) and characterization of palladium nano-particles stabilized with protecting ligands (L1 an L2) containing a combination of sulphur/selenium and 'N' donors.…”

Palladium complexes derived from benzoylthiourea ligands: Synthesis, crystal structure, and catalytic application in Suzuki C–C coupling reactions

“…These results also indicate that our thiourea ligands are highly capable of stabilizing the active catalyst; in other words, synthesized benzoylthioureapalladium complexes are necessary intermediates for the formation of active Pd(0) species in the reaction medium. [65,68,69] After determining the catalytic pathway, the reusability of black precipitates that produced by precatalyst [PdCl 2 (HL 2 -κS) 2 ] during the reaction under the optimized conditions was studied. At the end of each reaction, the resulting black precipitates were recovered by centrifugation and washed with chloroform, methanol, and water, respectively.…”

Functionalization of graphene oxide with a hybrid P, N ligand for immobilizing and stabilizing economical and non-toxic nanosized CuO: an efficient, robust and reusable catalyst for the C–O coupling reaction inO-arylation of phenol

“…in the head groups according to their applications. 10–15 It is assumed that, during the catalytic process, the role of the donor sites ( i.e. , N/P/O/S/Se/Te) and steric architecture of the ligand is as crucial as in the case of catalysis with homogeneous molecular complexes.…”